A corrugated board printing press is provided with a plurality of printing rolls to realize multi color printing. In order to avoid disadvantages such as misregistration, these printing rolls must be driven so as to synchronize their phases with each other. In order to maintain the phase relationship between these rolls unchanged, they have heretofore been coupled and interlocked with each other through a transmission such as belts and/or gears so as to be driven from a single motor having a variable speed and a large capacity. This arrangement however requires breaking the interlocking relation between the printing rolls when replacing plate cylinders installed on the printing rolls or maintaining the printing press and then recoupling them together into an operable state. This recoupling requires a great deal of work so that the gears are properly re-engaged with each other in order to keep the phase relationship between the printing rolls synchronous.
U.S. Pat. No. 4,527,788 to Masuda, filed on Aug. 1, 1984, discloses a printing press making use of a sectional servodrive method to overcome the above-described disadvantages. This apparatus comprises, on each printing roll, a DC drive motor having a variable speed, a zero point sensor for detecting a zero point marked on the roll to determine the revolution angle of the roll, a tachometer generator for detecting the speed of the DC drive motor and a pulse generator for generating pulses at a preset rate per predetermined revolution angle of the DC drive motor. First, the initial phase for each roll is determined by the zero point sensor to set it to a desired value. A speed command common to the individual DC drive motors is converted by a V/F converter to a reference pulse signal. This reference pulse signal is integrated and compared with an integrated pulse signal from the pulse generator, thereby determining a deviation. This deviation corresponds to the difference between the ideal and actual phases of the printing roll. Using an analog computer, the F/V-converted reference pulse signal is compared with the revolution speed of the DC drive motor to determine a servo-controlling value. Further, the level of servo-controlling is adjusted according to the degree of the phase deviation, whereby the DC drive motor is servo-controlled.
In FIG. 4 is shown an illustrative system obtained by further improving on the system disclosed in U.S. Pat. No. 4,527,788. FIG. 4 is a block diagram illustrating the construction of a synchronous phase-control system for printing rolls in a corrugated board printing press having, for example, 3 printing rolls.
Three printing rolls 1.sub.1, 1.sub.2, and 1.sub.3 are driven by servomotors 13.sub.1, 13.sub.2 and 13.sub.3, respectively. Pulse encoders 14.sub.1, 14.sub.2 and 14.sub.3 respectively connected to servomotors 13.sub.1, 13.sub.2 and 13.sub.3 output positional feedback pulse signals 10.sub.1, 10.sub.2 and 10.sub.3, respectively, according to the revolution of their corresponding servomotors 13.sub.1, 13.sub.2 and 13.sub.3. Positional feedback pulse signals 10.sub.1, 10.sub.2 and 10.sub.3 are inputted as feedback N.sub.FB in respective servo-drivers 12.sub.1, 12.sub.2 and 12.sub.3 through their corresponding F/V converters 8 and at the same time, also in their corresponding deviation counters 5. The term "synchronous phase-control" as used herein means that in this apparatus of the sectional servodrive system, the phase relationship between the rotors of the individual servomotors at the beginning of operation is kept unchanged during operation.
For this purpose, reference positional command pulse signal 9 is generated by pulse generator 3 according to speed command v.sub.ref inputted from speed setter 2. Any deviation between this signal and positional feed back pulse signal 10.sub.1 is detected by deviation counter 5 and outputted as positional deviation signal 15. Deviation counter 5 comprises phase pulse counter 5a, pulse computing circuit 5b and reference pulse counter 5c and is conventionally known. After positional deviation signal 15 is D/A-converted by D/A converter 6, the gain of the analog signal thus converted is adjusted by analog regulator 7. The analog signal thus adjusted is added to an analog speed command converted from reference positional command pulse signal through F/V converter 4. The sum is given as revolution speed command 11 for servomotor 13.sub.1 to servodriver 12.sub.1, whereby servodriver 12.sub.1 serves to drive servomotor 13.sub.1. To other servomotors 13.sub.2 and 13.sub.3, respective revolution speed commands 11.sub.2 and 11.sub.3 are also given by control units similar to that described above, so that each of servomotors 13.sub.1 to 13.sub.3 is synchronously phase-controlled in such a manner that the deviation of the actual revolution from the positional command generated by common speed command v.sub.ref becomes zero.